To further explain this, a SELECT CASE statment is just a tidier version of an IF statement - the one I wrote above is the equivalent to

IF Text1.Text="AAAA" Then
Text1.Text="BBBB"
ElseIf Text1.Text="BBBB" Then
Text1.Text="CCCC"
Else
Text1.Text="AAAA"
End If

The bit after the SELECT CASE statement is evaluated by VB - then it looks for the appropriate CASE line that matches the evaluation; eg;

SELECT CASE myAge
CASE IS <5
MsgBox "Under 5"
CASE = 10
MsgBox "10 Years Old"
CASE IS >30
Msgbox "Over 30"
CASE ELSE
Msgbox "Another age!"
END SELECT

This would display "Under 5" if myAge was less than 5, "10 Years Old" if myAge=10, "Over 30" if myAge was greater than 30, and "Another Age" if myAge didn't fall into any of these categories.
Hope this helps to explain it a bit.